The invention relates to a clamping device for an injection molding machine for plastics.
EP 0658 136 B1 discloses a clamping unit for molding tools of injection molding machines, including a clamping system in the form of a toggle mechanism, disposed between the moving platen and an end platen, for displacing the moving platen. Several so-called five-point toggle lever systems are coupled with a common crosshead. A threaded spindle is connected in fixed rotative engagement upon the crosshead and engages a nut which is immobile in axial direction but received in the end platen for rotation. The rotary drive is implemented by coupling the nut to a hollow shaft of an electric motor which is flange-mounted to the outside of the end platen. The hollow shaft is internally so dimensioned as to be suitable to easily receive the entire length of the threaded spindle, when the threaded spindle extends rearwards out of the nut. The toggle lever systems are in symmetric relationship to the force axis of the clamping unit, and the threaded spindle, the spindle nut and the electric motor with its hollow shaft are in alignment with the force axis of the clamping unit. A similar system is described in DE-PS 195 24 314 C1.
These systems have shortcomings relating to a comparably long construction of the clamping device because the electric motor is arranged outside the end platen and the inner dimension of the hollow shaft is suited to the spindle length.
Generic U.S. Pat. No. 5,804,224 discloses (see FIG. 1) the securement of the hollow-shaft motor to the crosshead of the toggle type clamping unit and to drive with the rotor a spindle which is in engagement with a spindle nut that is non-rotatably fixed on the backside of the end platen. As the rotor is rotated, the spindle is caused to rotate and the unit of spindle and hollow-shaft motor is moved axially to the rear and the front, as a consequence of the engagement with the fixed spindle nut, so that the toggle mechanism is operated. This embodiment has also the drawback that the clamping device demands a relative large space because the spindle juts out considerably from the backside of the end platen, when the clamping unit is open.